Ettrich founded and furthered the LyX project in 1995, initially conceived as a university term project. LyX is a graphical frontend to LaTeX.

Since LyX's main target platform was Linux, he started to explore different ways to improve the graphical user interface, which ultimately led him to the KDE project. Ettrich founded KDE in 1996, when he proposed on Usenet a "consistent, nice looking free desktop-environment" [sic] for Unix-like systems using Qt as its widget toolkit.[2][3]